Believe it or not, this sort of oil consumption is within spec for many manufacturers (not sure about Subaru though).

Some cars burn 1L per 1000km, some burn none at all. Ask BMW M3 or Porsche owners how much oil their cars burn

As long as its making power, and not smoking visibly out of the exhaust, its nothing to worry about and it doesnt warrant an engine rebuild. Make sure you rule out external leaks before worrying about oil consumption.